Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because of its non-impact, low-noise characteristics, its use of plain paper, and its avoidance of toner transfer and fixing. Ink jet printing mechanisms can be categorized by technology as either drop on demand ink jet (DOD) or continuous ink jet (CU).
Continuous inkjet printing uses a pressurized liquid source that produces a stream of drops some of which are selected to contact a print media (often referred to a “print drops”) while other are selected to be collected and either recycled or discarded (often referred to as “non-print drops”). For example, when no print is desired, the drops are deflected into a capturing mechanism (commonly referred to as a catcher, interceptor, or gutter) and either recycled or discarded. When printing is desired, the drops are not deflected and allowed to strike a print media. Alternatively, deflected drops can be allowed to strike the print media, while non-deflected drops are collected in the capturing mechanism.
Drop on demand printing only provides drops (often referred to a “print drops”) for impact upon a print media. Selective activation of an actuator causes the formation and ejection of a drop that strikes the print media. The formation of printed images is achieved by controlling the individual formation of drops. Typically, one of two types of actuators is used in drop on demand printing devices—heat actuators and piezoelectric actuators. When a piezoelectric actuator is used, an electric field is applied to a piezoelectric material possessing properties causing a wall of a liquid chamber adjacent to a nozzle to be displaced, thereby producing a pumping action that causes an ink droplet to be expelled. When a heat actuator is used, a heater, placed at a convenient location adjacent to the nozzle, heats the ink. Typically, this causes a quantity of ink to phase change into a gaseous steam bubble that displaces the ink in the ink chamber sufficiently for an ink droplet to be expelled through a nozzle of the ink chamber.
In some applications it may be desirable to use an ink that is not aqueous and, as such, does not easily form a vapor bubble under the action of the heater. Heating some inks may cause deterioration of the ink properties, which can cause reliability and quality issues. As described in U.S. Pat. No. 4,480,259 and U.S. Pat. No. 6,705,716, one solution is to have two fluids in the print head with one fluid dedicated to respond to an actuator, for example, to create a vapor bubble upon heating, while the other fluid is the ink. The performance capabilities of these types of print heads are often limited due to the resistance of the membrane or diaphragm that separates the actuator fluid from the ink which reduces the amount of volumetric displacement that occurs in ink chamber as a result of the pressure caused by the vaporization of the actuator fluid. Although U.S. Pat. No. 4,480,259 and U.S. Pat. No. 6,705,716 both describe flexible diaphragms, it is well understood by one skilled in the art that it is difficult to manufacture a micro-fluidics device such as an ink jet print head using conventional MEMS technology while incorporating a sufficiently elastic material for use as a diaphragm. Additionally, repeated cycles of stretch and relax cause material fatigue in the diaphragm resulting in reduced device reliability and poor device performance.
As such, there is an ongoing effort to increase the reliability and performance of print heads that include two fluids and a flexible membrane.